1. Field of the Invention
The present invention relates to an image forming apparatus, such as a copying machine, which is capable of designating a specific portion of a picture on a document, for example, and obtaining a copied picture in which a part of the picture corresponding to the designated specific portion is erased.
2. Description of the Related Art
Some types of recent electronic copying machines have various useful functions. One of those functions is an image designating function by which a specific portion of a picture on a document is designated before it is copied. Using the image designating function, the designated specific portion can be erased when it is copied. This specific portion erasing function is called trimming or masking.
In some copying machines of this type, a marker pen is used for designating a specific picture area to be edited on a document. The color of the maker pen is of the type in which a photosensitive drum of the copying machine is very sensitive to a mark written by the marker pen. In use, before the copying operation of the copying machine, the document is scanned by a scanner to recognize the marked picture area. To enhance the discrimination of the marked area from the remaining area of the picture, for example, color filters of the same color as that of the mark and of the color different from the same are inserted in an optical path in the scanner, every the marked area is scanned. The image data picked up through the scanning operation is stored into a memory. Then, the image data is read out and subjected to a proper arithmetic operation, so that the copying machine electronically recognized the designated specific area of the copied picture.
To realize other various functions, the designation of specific areas by the marker pen has been employed.
In the conventional copying machines of this type, for the above scanning, the color filters are properly switched during a reciprocal motion of the scanner. Therefore, the scanning direction as viewed by one filter is reverse to that by the other. To cope with this the image data collected through one of the color filters is reversed and stored. Alternatively, the image data collected through those filters are stored as intact. When it is read out, one of the two types of the image data is reversed. This approach brings about intricated signal processings.